1. Field of the Invention
The present invention relates to a controller for a motor and a control method for a motor adapted to control the operations of a plurality of permanent magnet field type rotary motors.
2. Description of the Related Art
Hitherto, there has been known a motor which has a first rotor and a second rotor concentrically provided around a rotating shaft of a permanent magnet field type rotary motor and which is adapted to conduct field control by changing a phase difference between the first rotor and the second rotor according to a rotational velocity thereby to change an induced voltage constant (refer to, for example, Japanese publication of unexamined patent application No. 2002-204541).
In such a conventional motor, the first rotor and the second rotor are connected through the intermediary of a member that is displaced in the radial direction when subjected to a centrifugal force. The motor is configured such that, when the motor is in a halting state, the magnetic poles of the permanent magnets disposed in the first rotor and the magnetic poles of the permanent magnets disposed in the second rotor are oriented in the same direction, providing largest magnetic fluxes of the fields, i.e., a largest induced voltage constant of the motor. As the rotational velocity of the motor increases, the phase difference between the first rotor and the second rotor increases due to a centrifugal force, thus reducing the magnetic fluxes of the fields, i.e., reducing the induced voltage constant of the motor.
FIG. 16 shows a range in which the field of the motor need to be weakened, the axis of ordinates indicating output torque Tr and the axis of abscissas indicating a number of revolutions N. In FIG. 16, a character “u” denotes an orthogonal line of the motor. The line u is formed by connecting the points at which a phase voltage of the motor becomes equal to a supply voltage, depending on a combination of the number of revolutions and an output torque when the motor is actuated without carrying out the field weakening control. A character X in the figure denotes a range in which the field weakening is not required, while a character Y denotes a range in which the field weakening is required.
As shown in FIG. 16, the range Y in which the field weakening is necessary is determined by the number of revolutions N and the output torque Tr of the motor. Hence, in the conventional field weakening control, which depends merely on the number of revolutions, a change of an induced voltage constant of the motor has inconveniently become excessive or insufficient with respect to a required field weakening control amount.
The aforesaid motor that changes the phase difference between the first rotor and the second rotor according to the number of revolutions allows an operating condition of the motor to be changed according to a change in the number of revolutions of the motor. However, in a system adapted to operate a plurality of motors in cooperation, such as a hybrid car wherein front wheels and rear wheels thereof are driven by separate motors, it is required to change the operating condition of each motor by considering differences in operating states, including a loss incurred in each motor and the temperature thereof.
When individually setting the operating condition of each motor according to the number of revolutions of the motor, it is impossible to change the operating condition of each motor while considering differences in the operating states, including loss and temperature, between the motors.